Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
REVIEW
Domestication evolution, genetics and genomics in wheat
Junhua H. Peng • Dongfa Sun • Eviatar Nevo
Received: 10 January 2011 / Accepted: 15 June 2011 / Published online: 9 July 2011
� Springer Science+Business Media B.V. 2011
Abstract Domestication of plants and animals is
the major factor underlying human civilization and is
a gigantic evolutionary experiment of adaptation and
speciation, generating incipient species. Wheat is one
of the most important grain crops in the world, and
consists mainly of two types: the hexaploid bread
wheat (Triticum aestivum) accounting for about 95%
of world wheat production, and the tetraploid durum
wheat (T. durum) accounting for the other 5%. In this
review, we summarize and discuss research on wheat
domestication, mainly focusing on recent findings in
genetics and genomics studies. T. aestivum originated
from a cross between domesticated emmer wheat
T. dicoccum and the goat grass Aegilops tauschii,
most probably in the south and west of the Caspian
Sea about 9,000 years ago. Wild emmer wheat has
the same genome formula as durum wheat and has
contributed two genomes to bread wheat, and is
central to wheat domestication. Domestication has
genetically not only transformed the brittle rachis,
tenacious glume and non-free threshability, but also
modified yield and yield components in wheat. Wheat
domestication involves a limited number of chromo-
some regions, or domestication syndrome factors,
though many relevant quantitative trait loci have been
detected. On completion of the genome sequencing of
diploid wild wheat (T. urartu or Ae. tauschii),
domestication syndrome factors and other relevant
genes could be isolated, and effects of wheat
domestication could be determined. The achieve-
ments of domestication genetics and robust research
programs in Triticeae genomics are of greatly help in
conservation and exploitation of wheat germplasm
and genetic improvement of wheat cultivars.
Keywords Cultivated wheat � Wild emmer wheat �Evolution and domestication � Major domestication
gene � Domestication-related QTL � Domestication
syndrome factor
Abbreviations
Mya Million years ago
BP Years before present
SSR Simple sequence repeat
J. H. Peng (&)
Key Laboratory of Plant Germplasm Enhancement and
Specialty Agriculture, and Wuhan Botanical Garden,
Chinese Academy of Sciences, Moshan, Wuhan 430074,
Hubei, China
e-mail: [email protected]
J. H. Peng
Department of Soil and Crop Sciences, Colorado State
University, Fort Collins, CO 80523-1170, USA
D. Sun
College of Plant Science and Technology, Huazhong
Agricultural University, Wuhan 430070, Hubei, China
e-mail: [email protected]
E. Nevo
Institute of Evolution, University of Haifa, Mount Carmel,
Haifa 31905, Israel
e-mail: [email protected]
123
Mol Breeding (2011) 28:281–301
DOI 10.1007/s11032-011-9608-4
Br Brittle rachis
Tg Tenacious glume
Ppd Photoperiod response
QTL Quantitative trait locus
DSF Domestication syndrome factor
AFLP Amplified fragment length polymorphism
Introduction
Domestication is the outcome of a selection process
that results in the increased adaptation of plants or
animals to cultivation or rearing and use by humans
(Brown 2010). It is a gigantic evolutionary experi-
ment of adaptation and speciation, generating incip-
ient species (Darwin 1905). It has been performed by
humans primarily during the last 10,000 years (Zoh-
ary and Hopf 2000; Feldman and Kislev 2007), and
has led to adaptive syndromes fitting human ecology
(Harlan 1992). Human sedentism, urbanization, cul-
ture and an unprecedented population explosion have
depended, to a large extent, on domestication and the
related agricultural economies. Human behaviours
and plant genetic adaptations have been entangled
during the domestication (Allaby 2010; Fuller et al.
2010). Domestication makes all the cultivars, includ-
ing wheat, human-dependent, capable of surviving
only under cultivation in human agricultural niches to
meet human needs (Gustafson et al. 2009; Nevo
2011).
Wheat is the universal cereal of Old World
agriculture (Zohary and Hopf 2000) and the world’s
foremost crop plant (Feldman et al. 1995; Gustafson
et al. 2009), followed by rice and maize. Modern
wheat cultivars usually refer to two species: hexa-
ploid bread wheat, Triticum aestivum (2n = 6x = 42,
AuAuBBDD), and tetraploid, hard or durum-type
wheat, T. durum (2n = 4x = 28, AuAuBB) used for
macaroni and low-rising bread. Other species are
relict (for a detailed account see Zohary and Hopf
2000; Gill et al. 2006, 2007; Feldman and Kislev
2007). Bread wheat accounts for about 95% of world
wheat production, and durum wheat the other 5%.
Today, wheat ranks first in world grain production
and accounts for more than 20% of total human food
calories. Wheat is extensively grown on 17% of all
crop areas, in the temperate, Mediterranean-type and
subtropical parts of both hemispheres, from 67�N in
Norway, Finland and Russia to 45�S in Argentina. It
is the staple food for 40% of the world’s population,
mainly in Europe, North America and the western and
northern parts of Asia (http://www.faostat.fao.org;
http://www.croptrust.org).
Wheat is a superb model organism for the
evolutionary theory of allopolyploid speciation,
adaptation and domestication in plants (Gustafson
et al. 2009). Its domestication caused substantial
genetic erosion and that erosion was reinforced
during modern breeding processes, and thus increased
susceptibility and vulnerability to environmental
stresses, pests and diseases (Nevo 2009, 2011; Fu
and Somers 2009). Hence, its future genetic improve-
ment as a high-quality nutritional food is paramount
for feeding the ever-increasing human population.
The best strategy for wheat improvement is to utilize
the adaptive genetic resources of the wild progeni-
tors, wild emmer T. dicoccoides and other wheat
relatives (Feldman and Sears 1981; Nevo and Beiles
1989; Nevo et al. 2002; Nevo 2011).
The economic importance of wheat has triggered
intense cytogenetic and genetic studies in the past
decades that have resulted in a wealth of information
and tools which have been used to develop wheat
cultivars with increased yield, improved quality and
enhanced biotic and abiotic stress tolerance (Carver
2009). In contrast, genomics in wheat has lagged
behind other plant species, and is hampered by the
huge genome sizes (15,961 Mb for bread wheat;
11,660 Mb for durum wheat; Bennett and Leitch
2010) and complexity of the genomes. Recently,
however, the situation has changed dramatically and
the convergence of several technological develop-
ments has led to the development of new and more
efficient resources that support the establishment of
robust genomic programs in wheat (Feuillet and
Muehlbauer 2009). These new capabilities will
provide a better understanding of wheat domestica-
tion evolution and support the improvement of
agronomically important traits in this essential spe-
cies (Feuillet and Muehlbauer 2009; Paux and
Sourdille 2009). Therefore, we are currently witness-
ing a pinnacle of genomic research into the process of
domestication itself, particularly the specific
major and minor genes involved (Brown 2010), and
the epic effort to sequence the wheat genome. In this
review we summarize and discuss the most recent
282 Mol Breeding (2011) 28:281–301
123
achievements of wheat domestication studies, espe-
cially in the fields of genetics and genomics.
Evolution of wheat
The family Poaceae (grasses) evolved 50–70 million
years ago (Mya) (Kellogg 2001; Huang et al. 2002) and
the sub-family Pooideae including wheat, barley and
oats diverged around 20 Mya (Inda et al. 2008). Wild
diploid wheat (T. urartu, 2n = 2x = 14, genome
AuAu) hybridized with the B genome ancestor that is
the closest relative of goat grass (Aegilops speltoides,
2n = 2x = 14, genome SS) 300,000–500,000 years
before present (BP) (Huang et al. 2002; Dvorak and
Akhunov 2005) to produce wild emmer wheat (T.
dicoccoides, 2n = 4x = 28, genome AuAuBB). The
earliest evidence that man collected and used these
cereals is from Ohalo II, a permanent site of epipaleo-
lithic (19,000 BP) hunter-gatherers on the southwest-
ern shore of the Sea of Galilee, Israel (Feldman and
Kislev 2007). Here, Kislev et al. (1992) found grains of
wild barley and wild emmer, and Piperno et al. (2004)
presented evidence for grain processing and baking of
flour. About 10,000 BP, hunter-gatherers began to
cultivate wild emmer. Subconscious selection gradu-
ally created a cultivated emmer (T. dicoccum,
2n = 4x = 28, genome AuAuBB) that spontaneously
hybridized with another goat grass (Ae. tauschii,
2n = 2x = 14, genome DD) around 9,000 BP to
produce an early spelt (T. spelta, 2n = 6x = 42,
genome AuAuBBDD) (http://www.newhallmill.org.
uk/wht-evol.htm; Kihara 1944; McFadden and Sears
1946; Kerber 1964; Kislev 1980; Dvorak et al. 1998;
Matsuoka and Nasuda 2004). This cross took place
after emmer wheat cultivation expanded eastwards
from the Fertile Crescent to the natural habitat of Ae.
tauschii, and occurred probably south and west of the
Caspian Sea (Nesbitt and Samuel 1996; Salamini et al.
2002; Giles and Brown 2006). About 8,500 BP, natural
mutation changed the ears of both emmer and spelt to a
more easily threshed type that later evolved into the
free-threshing ears of durum wheat (T. durum) and
bread wheat (T. aestivum) (Fig. 1). However, recent
experimental evidence suggests that T. spelta is not the
ancestral form of free-threshing common wheat
(Dvorak et al. 2006). Apparently, the sources of culti-
vated wheat ancestry are complicated by multiple
factors including gene flow from wild cereals (Dvorak
et al. 2011).
Domestication of wheat
According to the history of wheat evolution described
above, only wild einkorn and wild emmer wheats
were subjected to domestication selection. The
hexaploid common or bread wheat was not directly
derived from a wild progenitor through domestication
selection but from T. turgidum spp. dicoccon (Dvorak
et al. 2011). Therefore, we only review here the
domestication studies on diploid einkorn wheat and
tetraploid emmer wheat.
There are two wild diploid Triticum species
recognized: T. boeoticum (AbAb) and T. urartu
(AuAu). They have crossing barriers between them
(Johnson and Dhaliwal 1976) and differ in plant
morphology (Gandilian 1972; Dorofeev et al. 1979)
and at biochemical and molecular marker loci
(Johnson 1975; Dvorak et al. 1998, 2011; Kilian
et al. 2007). The diploid einkorn wheat T. monococ-
cum was one of the first crops domesticated in the
Fertile Crescent from the wild progenitor species
T. boeoticum. The domestication of einkorn wheat
occurred in the Karacadag mountain range in south-
east Turkey (Heun et al. 1997). During the last
5,000 years, einkorn was basically replaced by tetra-
ploid and hexaploid wheats. Einkorn is currently a
relict crop and is only grown on a very small scale as
Wild Diploid Wheat Triticum urartu
Goat Grass 1Aegilops speltoides
Years Before Present (yr BP)
Goat Grass 2Aegilops tauschii
Wild Emmer Triticum dicoccoides
300,000-500,000
Wild
10,000
9,000
8,500
Cultivated
AABB
AA BB
DD
Cultivated Emmer Triticum dicoccum
SpeltTriticum spelta
Bread Wheat Triticum aestivum
Macaroni Wheat Triticum durum
AABB
AABBDD
AABBDD
‘Hulled’ or enclosed grains
Free-threshing grains
AABB
Fig. 1 The evolution of wheat from the prehistoric Stone Age
grasses to modern macaroni wheat and bread wheat (repro-
duced from http://www.newhallmill.org.uk/wht-evol.htm)
Mol Breeding (2011) 28:281–301 283
123
feed in a few Mediterranean countries (Nesbitt and
Samuel 1996; Perrino et al. 1996).
The other wild diploid Triticum species, T. urartu
(AuAu), occurs in parts of the Fertile Crescent
(Zohary and Hopf 2000), and has played an essential
role in wheat evolution though it has never been
domesticated. T. urartu contributed the Au genome to
all tetraploid and hexaploid wheats (Dvorak et al.
1993). There are also two wild tetraploid wheat
species known as T. dicoccoides (AuAuBB) and
T. araraticum (AuAuGG). Tests using DNA molec-
ular markers show that wild tetraploid wheat did
participate in the evolution of hexaploid wheat
(Dvorak et al. 2011). T. dicoccoides, wild emmer,
grows naturally all over the Fertile Crescent. Wild
emmer wheat was discovered in 1906 by Aaron
Aaronsohn in Israel (Aaronsohn and Schweinfurth
1906). The domesticated form of T. dicoccoides is
known as T. dicoccum (emmer, AuAuBB).
Emmer is believed to have been domesticated
probably in southeast Turkey (Ozkan et al. 2002,
2005, 2010; Mori et al. 2003; Luo et al. 2007; Dvorak
et al. 2011). Phylogenetic analysis indicates that two
different races of T. dicoccoides exist: the western
one, colonizing Israel, Syria, Lebanon and Jordan;
and the central–eastern one, which has been fre-
quently sampled in Turkey and rarely in Iraq and
Iran. It is the central–eastern race that has played the
role as progenitor of the domesticated germplasm
(Ozkan et al. 2002, 2010; Mori et al. 2003; Luo et al.
2007), which indicates that the Turkish Karacadag
population has a tree topology consistent with that of
the progenitor of domesticated genotypes. Based on
geographical distribution and molecular marker data,
Ozkan et al. (2010) most recently suggested that the
‘‘dispersed-specific’’ domestication model proposed
for einkorn might appropriately fit emmer. The model
assumes pre-adaptation of a wild emmer race for
cultivation. This race was spread to several locations
in the Fertile Crescent before being domesticated at
several sites.
However, the allozymic study of Nevo and Beiles
(1989) found no evidence for two races of T.
dicoccoides. Archaeological findings from the period
of 10,300–9,500 BP shows that wild emmer was first
cultivated in the southern Levant. Domesticated
emmer appeared several hundred years later, i.e.,
9,500–9,000 BP, and for a millennium or more was
grown in a mixture with wild emmer in many
Levantine sites. After the appearance of domesticated
emmer, types with naked, free-threshing grains
emerged during the period 9,000–7,500 BP. These
archaeological findings of wild emmer cultivation
and domestication do not support the hypothesis of
domestication within a small core area, but rather
demonstrate the polycentric origin of agriculture in
the Levant (Kislev et al. 1992; Feldman and Kislev
2007). As reviewed most recently by Ozkan et al.
(2010), archaeobotanical studies strongly suggest that
wild emmer was possibly twice and independently
taken into cultivation, in the southern Levant and in
the northern Levant. The model of multiple-site
independent domestication of wild emmer across the
Levant seems more realistic. According to this
model, the genes for non-brittleness were transferred
to numerous wild emmer genotypes through numer-
ous spontaneous hybridizations and spontaneous
mutations, followed by human selection. Conse-
quently, domesticated emmer wheat evolved as
polymorphic populations rather than as single geno-
types (Feldman and Kislev 2007). Domesticated
emmer was once the main crop for bread-making in
ancient Egypt. Emmer cultivation has significantly
declined and can be found only in a few traditional
farming communities, mainly in Russia and Ethiopia.
Durum wheat (T. durum) derived from T. dicoccum
(Damania 1998) is a free-threshing naked wheat and
is widely cultivated today for pasta production.
Speed of wheat domestication
Conventionally, wheat domestication studies have
focused on a few qualitative traits (brittle rachis,
tough glume and free-threshing) controlled by single
major genes (Br/br, Tg/tg and Q/q; see Fig. 2 and Gill
et al. 2007). If ancient wheat breeders or farmers only
selected the non-shattering or indehiscent, soft glume
and free-threshing mutants in the wild wheat popu-
lations, the wheat plant would have been domesti-
cated in a very short period, or the domestication
should have been a rapid event. Hillman and Davies
(1990) performed natural selection of barley, einkorn
and emmer wheat under primitive farming prac-
tices and concluded that perhaps only 20–30 years
would be enough to completely domesticate
these plants. Honne and Heun (2009) validated this
viewpoint.
284 Mol Breeding (2011) 28:281–301
123
However, the fact that remains of wild and
domesticated forms of the same plant overlapping
for a long time (up to 3,000 years) is inconsistent
with rapid domestication (Tanno and Willcox 2006;
Balter 2007; Willcox et al. 2008). Indehiscence took
over one millennium to become an established event
(Tanno and Willcox 2006, Fig. 3). This means that
early farmers possibly did not focus only on indehis-
cence, but also on other important quantitative
traits—spike size, heading date/growth duration,
plant height, grain size, etc.—in the harvesting
process of wild wheat. Measurements taken from
ancient grains demonstrate that the size of wheat and
barley grains remained essentially the same between
9,500 and 6,500 BP (Willcox 2004). Therefore,
selection for large cereal grains was slow because
grain size was controlled by polygenes (Peng et al.
2003).
If early farmers harvested spikes after the ears
began to shatter, indehiscent mutants would be
rapidly adopted. But farmers probably harvested
before the spikelets fell, to avoid loss, and paid
attention to important agronomic and economic traits
(yield and yield components, plant height and
heading date, etc.); thus indehiscence was not
advantageous. Furthermore, when crops failed, farm-
ers would have had to gather spikes from the wild.
These two practices lowered the probability of the
rare indehiscent mutant being selected. Domestica-
tion was a series of events occurring at different
places over thousands of years (Feldman and Kislev
2007), during which wild wheat persisted in culti-
vated fields. Therefore, the process of wheat domes-
tication was slow, spanned over one thousand years,
occurred in multiple sites of the Fertile Crescent, and
fitted a gradualist and multi-site model (Fig. 3, Tanno
and Willcox 2006; Feldman and Kislev 2007). This
multi-site and long-term domestication seems more
realistic than the fast domestication.
Effects of domestication on genetic diversity
Domestication of plants and animals usually results in
a reduction of genetic diversity involving the whole
genome (Doebley 1989; Gepts 2004; Ross-Ibarra
et al. 2007; Fu and Somers 2009). The domesticate
acquires improved fitness for human purpose often at
the expense of survival in nature, and a mutualistic
relationship evolves between humans and their crops
through the domestication process (Gepts 2004). One
of the correlated changes in the genome is conse-
quential phenomena, such as loss of diversity,
selective sweeps and adaptive diversification (Brown
2010). The bottleneck reduces diversity in neutral
genes, but selection decreases diversity beyond that
caused by the bottleneck alone (Ross-Ibarra et al.
2007). Several demographic and selective events
occurred during the domestication of wheat from
T. dicoccoides. Haudry et al. (2007) analyzed
Fig. 2 Wheat spikes
showing a brittle rachis,
(b to d) non-brittle rachis,
(a and b) hulled grain, and
(c and d) naked grain.
a Wild emmer wheat
(T. dicoccoides),
b domesticated emmer (T.dicoccum), c durum (T.durum), and d common
wheat (T. aestivum). Whitescale bars represent 1 cm.
Letters at the lower rightcorner indicate the genome
formula of each type of
wheat. Gene symbols: Brbrittle rachis, Tg tenacious
glumes, and Q square head
(reproduced from
Dubcovsky and Dvorak
2007)
Mol Breeding (2011) 28:281–301 285
123
nucleotide diversity at 21 loci in wild and domesti-
cated, cultivated durum and bread wheats, and
revealed that diversity was further reduced in culti-
vated forms during domestication—by 69% in bread
wheat and 84% in durum wheat.
Demographic events can have dramatic effects on
the long-term effective size (Ne) of a population.
Reductions of Ne, typically referred to as genetic
bottlenecks, have usually led to decreased levels of
diversity in cultivated crops relative to their wild
progenitors (Buckler et al. 2001). Using simple
sequence repeat (SSR) marker data, Thuillet et al.
(2005) found a Ne of 32,500 individuals in wild
emmer wheat, 12,000 in the domesticated form, 6,000
in landraces and 1,300 in recent improved varieties of
tetraploid wheat. This decrease clearly demonstrates
the successive bottlenecks in durum wheat during
domestication and subsequent agronomic improve-
ment of the species.
Dubcovsky and Dvorak (2007) believe that high
mutation rates, together with buffering effects caused
by polyploidy, should enable hexaploid wheat to
enhance diversity. However, a genome-wide exami-
nation of 75 Canadian wheat (T. aestivum) cultivars
released from 1845 to 2004 examined by using 370
SSR markers indicated that allelic reduction occurred
in every part of the wheat genome and a majority of
the reduced alleles resided in only a few early
cultivars. The net reduction of the total SSR variation
in 20 recent cultivars was 17% (Fu and Somers
2009). Based on a large-scale single nucleotide
polymorphism (SNP) analysis in wheat, Akhunov
et al. (2010) suggest that ancestral species are the
primary source of genetic diversity in the young
polyploidy species, T. aestivum. Low effective
recombination resulting from self-pollination and a
genetic mechanism prohibiting homeologous chro-
mosome pairing during meiosis can cause diversity
loss in large chromosomal regions. Accumulation of
new mutations in older polyploid species, such as
wild emmer, results in increased diversity and its
more uniform distribution across the genome (Akhu-
nov et al. 2010). Based on the haplotype analysis of a
dimorphism locus (ABCT-A1a/b), Dvorak et al.
(2006) believe that T. aestivum in eastern Asia
conserved the gene pool of the original T. aestivum
more than wheat elsewhere, and diffusion of the
original T. aestivum from Transcaucasia or the
southwestern Caspian westward to eastern Turkey
would have resulted in sympatry with wild emmer
and potential for gene flow from wild emmer to T.
aestivum. Such gene flow unavoidably increased
genetic diversity in T. aestivum, and modified the
geographical pattern of wheat genetic diversity
(Dvorak et al. 2011). Analyses of linkage disequilib-
rium (LD) and SNP variation have showed that
breeding and selection had a different impact on each
wheat genome both within and among populations,
and revealed the highest extent of significant LD in
the wheat D-genome, which likely reflects the
Fig. 3 Modern examples of dehiscent wild einkorn wheat ear
(a) and spikelet (b). Detail of spikelet with smooth wild
abscission scar (c), indehiscent domestic ear (d), and detail of
spikelet with jagged break (e) are shown. The table (f) gives
relative frequencies of sub-fossil finds. Records from Aswad
and Ramad (van Zeist and Bakker-Heeres 1985) are of barley;
the other four sites are of wheat (reproduced from Tanno and
Willcox 2006)
286 Mol Breeding (2011) 28:281–301
123
episodes of recent introgression and population
bottleneck accompanying the origin of hexaploid
wheat (Chao et al. 2010). Therefore, modern breeding
does reinforce the genetic bottlenecks which started
with early domestication of wheat, but the dominant
mechanism of chromosome number reduction caused
by inversions and translocations in grasses could have
accelerated genome evolution in the polyploid Triti-
ceae (Luo et al. 2009), and it is vital to conserve
wheat germplasm and introduce genetic diversity into
wheat breeding programs from both landraces and
wild relatives.
Genetic and genomic dissection of qualitative
domestication traits
Recent genetic and genomic studies are summarized
for the following qualitative traits that have under-
gone domestication selection in wheat.
Brittle rachis
The breakage of rachis sheds seeds at maturity of any
wild forms of wheat. This trait is agriculturally
deleterious, and thus transformation of brittle rachis
(Br) to non-Br is perhaps the first symbol of domes-
tication in wheat (Peng et al. 2003). Loss of seed
shattering was a key event in the domestication of
major cereals (Konishi et al. 2006). The modification
of the brittle rachis trait has been critical for the origin
of agriculture and sedentary societies. In nature, the
spikelets of the wild ears fall apart at ripening through
fragmentation of the rachis (by shattering or disartic-
ulation). This mechanism is necessary for seed
dispersal and self-planting (Zohary and Hopfs 2000).
In a tough, non-brittle rachis the formation of fracture
zones at the rachis is suppressed until mature spikes
are harvested by man. It is thought that the spikes of
non-brittle mutated plants were consciously selected
by early farmers and that their frequency increased
constantly in cultivated fields. But this process was
slow and establishment of the non-brittle ancient
cultivar took over one millennium (Tanno and Will-
cox 2006; Balter 2007; Willcox et al. 2008). In a cross
between semi-wild wheat and T. spelta, three genes
interact to control three types of rachis fragility, i.e.,
semi-wild wheat-type, spelta-type and the tough
rachis of common wheat. Semi-wild wheat differs
from common wheat in rachis fragility. This wheat
also differs from other wheats with fragile rachis
(T. spelta, T. macha and T. vavilovii) in the pattern and
degree of rachis disarticulation (Cao et al. 1997).
The brittle rachis character is mapped to the
homeologous group 3 chromosomes in wheats
(Watanabe et al. 2002; Salamini et al. 2002; Watanabe
2005; Li and Gill 2006). In einkorn, this trait is under
the control of two genes that segregate 15 brittle to one
tough rachis in the F2 progeny of wild 9 domesticated
crosses (Sharma and Waynes 1980). Cao et al. (1997)
identified a single dominant gene, Br1, responsible for
rachis fragility in a feral form of T. aestivum from
Tibet. The gene was later localized on chromosome
3DS (Chen et al. 1998), as supported by studies of a
cross of T. dicoccoides 9 T. aestivum (Rong et al.
2000). This major distinguishing feature, brittle rachis,
between wild and domesticated emmer wheat is
controlled by two major genes, Br2 and Br3, on the
short arms of chromosomes 3A and 3B, respectively
(Cao et al. 1997; Chen et al. 1998; Watanabe and
Ikebata 2000; Nalam et al. 2006; Gill et al. 2007).
The previous studies show (1) multiple genetic
pathways controlling the trait(s); and (2) different
genetic origins of loci controlling shattering in
polyploids (Salamini et al. 2002). These consider-
ations, combined with the mapping of quantitative
trait loci (QTL) for shattering, allow analyses of the
microsyntenous relationships between these traits in
the Triticeae and other grasses. Br in T. dicoccoides
functions as an abscission layer in millet, seed
dispersal in sorghum and maize, and seed shedding
in rice (Peng et al. 2003).
Glume tenacity
Glume tenacity is another key trait closely related to
free-threshing habit and is modified by the domesti-
cation process in wheat (Gill et al. 2007). The wild
wheat floret is wrapped by tough glumes that make
spikes difficult to thresh, whereas cultivated wheats
have soft glumes and are free-threshing. Major and
minor mutations were involved in the evolution of the
free-threshing habit in hexaploid wheat (T. aestivum).
The non-free-threshing habit of semi-wild wheat
(T. tibetanum) was dominant over the free-threshing
habit of common wheat, and glume tenacity of semi-
wild wheat was controlled by a single gene in the
cross of semi-wild wheat with the wheat cultivar
Mol Breeding (2011) 28:281–301 287
123
Columbus. In the cross between semi-wild wheat and
T. spelta, the F2 and F3 populations did not segregate
for glume tenacity. Semi-wild wheat differs from
common wheat in glume tenacity (Cao et al. 1997).
The Tg1 locus on chromosome 2D confers the
free-threshing habit in hexaploid wheat (Kerber and
Rowland 1974). Genetic analysis showed that at least
two genes control the free-threshing trait in crosses
involving synthetic wheats (Villareal et al. 1996).
Jantasuriyarat et al. (2004) detected several QTL on
chromosomes 2A, 2B, 2D, 5A, 6A, 6D and 7B that
significantly affect the free-threshing characteristic.
However, the free-threshing habit was predominantly
affected by a QTL on chromosome arm 2DS
(corresponding to the Tg1 gene) and to a lesser
extent by a QTL on chromosome arm 5AL (corre-
sponding to the Q factor). Recently Tg1 was mapped
to a more precise location on 2DS (Nalam et al.
2007).
A recent study showed that the soft glume (sog)
gene in a diploid wheat relative, T. monococcum, was
found to be close to the centromere on the chromo-
some arm 2AS. But the tenacious glume (Tg) gene of
common wheat was located in the most distal region
on the chromosome arm 2DS. The different positions
suggest that the threshability mutations have different
evolutionary origins (Sood et al. 2009).
Free-threshing
The early wheat varieties were characterized by
hulled seeds that required drying to be liberated from
the chaff. When species characterized by a low
degree of glume tenacity and by fragile rachis and
free-threshing habit were selected by the farmers,
harvesting grains became efficient. Free-threshing
wheats have thinner glumes and paleas that allow an
early release of naked kernels. After threshing, free
grains are winnowed and stored ready for milling.
Free-threshing varieties, like tetraploid hard wheat
(T. durum) and hexaploid bread wheat (T. aestivum),
represent the final steps of wheat domestication.
Major and minor mutations have been proposed to
explain the evolution of the free-threshing habit in
wheat (McKey 1966; Jantasuriyarat et al. 2004). A
major gene Q located on the chromosome arm 5AL
inhibits speltoidy but also has pleiotropic effects on
rachis fragility and glume tenacity. All non-free-
threshing wild wheats carry the recessive q allele and
all free-threshing tetraploid and hexaploid wheats
carry the dominant Q allele. In T. aestivum, the
Q allele supports the formation of square-headed ears
with good threshability, besides inducing softening of
the glumes, reduction of ear length, more spikelets
per ear and toughness of the rachis (Sears 1954;
Snape et al. 1985; Kato et al. 1998, 2003; Gill et al.
2007). Disruption of the Q gene generates a q mutant
phenotype, known as speltoid type because q mutants
have tenacious glumes similar to that of spelt
(T. spelta; qq genotype). Bread wheat lines harboring
both Q and q alleles have intermediate phenotypes.
Muramatsu (1963) also showed that the q allele is
active by creating genotypes with one to five doses of
either Q or q alleles. He showed that a square-headed
hexaploid ear derives from either two doses of Q or
five doses of q.
The Tg gene controls the speltoid phenotype and
inhibits the expression of Q. The suppression of the
free-threshing character is thought to be due to a
partially dominant Tg allele on chromosome 2D,
derived from Ae. tauschii and thus resulting in
tenacious glumes. The conclusion is that free-thresh-
ing hexaploids have the genotype tgtg, QQ (Kerber
and Rowland 1974; Villareal et al. 1996; see Fig. 2).
In general, the Q gene is a major domestication
gene conferring spike shape and threshability in
wheat (Sears 1954; McKey 1966; Snape et al. 1985;
Kato et al. 1998, 2003; Luo et al. 2000). Faris et al.
(2005) and Gill et al. (2007) cloned the Q gene and
unravelled the structural and functional nature of the
free-threshing trait and other early domestication
events. The Q gene was shown to have sequence
similarity to the Arabidopsis APETALA2 gene, and is
thus a member of the AP2 family of plant-specific
transcriptional regulators (Faris and Gill 2002; Faris
et al. 2003, 2005; Gill et al. 2007). This gene family
regulates a diverse set of developmental traits in
plants, but especially those related to inflorescence
structure and flowering. The cultivated (Q) allele is
expressed at a higher level than the wild (q) allele,
and gene dosage analysis indicates that differences in
expression could be sufficient to explain the differ-
ence in phenotype. However, these alleles also differ
by a single amino acid change that affects protein
dimerization, suggesting that both regulator and
protein function changes could be involved (Doebley
et al. 2006). Further studies confirmed the association
(Simons et al. 2006) and demonstrated that ectopic
288 Mol Breeding (2011) 28:281–301
123
expression of Q in transgenic plants mimicked dosage
and pleiotropic effects of Q. Increased transcription
of Q was associated with spike compactness and
reduced plant height. Previous research suggested
that Q might have arisen from a duplication of
q (Kuckuck 1959). However, Simons et al. (2006)
repudiate this hypothesis and showed that most
probably Q arose through a gain-of-function
mutation.
Genetic and genomic analysis of quantitative
domestication traits
Additional traits modified during domestication and
the subsequent breeding process are quantitatively
inherited: e.g., grain yield, seed size, plant height and
heading date (Table 1). Furthermore, the spread of
domesticated wheat from the Fertile Crescent
required adaptation to new environments supported
by favorable alleles at critical genetic loci (Kilian
et al. 2009).
Seed size
The evolution from small-seeded wild plants with
natural seed dispersal to larger seeded non-shattering
plants is evident. In domesticated grasses, changes in
grain size and shape evolved prior to non-shattering
ears or panicles. Initial grain size increases may have
evolved during the first centuries of cultivation,
within perhaps 500–1,000 years (Fuller 2007). Seed
size was strongly selected in all domesticated cereals,
is under complex polygenic control, and the genes
have been mapped to seven or eight chromosomes
(Table 1, Elias et al. 1996; Peng et al. 2003; Gegas
et al. 2010). The major seed-size QTL correspond
closely in sorghum, rice and maize, and other QTL
correspond between two of these genera when the
taxa are compared in a pairwise fashion. Parallel
synteny existing between wheat and rice chromo-
somes indicates that all seed-size QTL detected in T.
dicoccoides correspond to their rice counterparts
(Peng et al. 2003).
Flowering time
Flowering time was also selected in the major cereals.
Short-day flowering wild grasses were transformed
into domesticates in which flowering time was
unaffected by day length (Buckler et al. 2001).
Heading date/flowering time is an important criterion
for regional adaptation in all cereals. The control of
heading date is critical for reproductive success and
Table 1 Quantitative trait loci related to domestication in wheat
Trait Number of
QTL effects
Residing chromosomea Reference
Seed size/weight 7 1A, 2A, 3A, 4A, 7A, 5B, 7B Elias et al. (1996)
8 1B, 2A, 4A, 5A, 5B, 6B, 7A, 7B Peng et al. (2003)
8 1B, 2A, 3A, 3B, 4B, 5A, 6A, 7A Gegas et al. (2010)
Flowering time 4 2A, 4B, 5A, 6B Peng et al. (2003)
Grain yield 8 1B, 2A, 3A, 5A, 5B Peng et al. (2003)
3 3A, 4A, 5A Araki et al. (1999), Shah et al. (1999),
Kato et al. (2000), Campbell et al. (2003)
Plant height 4 5A, 7B Peng et al. (2003)
Spike number/plant 7 1B, 2A, 2B, 5A, 7A Peng et al. (2003)
Spike weight/plant 10 1B, 2A, 3A, 5A, 5B, 7A Peng et al. (2003)
Single spike weight 5 1B, 2A, 3A, 5A Peng et al. (2003)
Kernel number/plant 9 1B, 2A, 3A, 5A, 5B, 7A Peng et al. (2003)
Kernel number/spike 7 1B, 2A, 3A, 5A, 6B Peng et al. (2003)
Kernel number/spikelet 7 1B, 2A, 3A, 5A, 5B, 7B Peng et al. (2003)
Spikelet number/spike 6 1B, 2A, 5A, 6B Peng et al. (2003)
a The bold-font chromosome carry a pair of linked QTL
Mol Breeding (2011) 28:281–301 289
123
has a major impact on grain yield in Triticeae. Wild
progenitors of domesticated cereals are well adapted
to the prevailing environmental conditions in the
Fertile Crescent. The first cereals domesticated in this
region presumably showed the photoperiodic and
vernalization phenotypes of their progenitors. How-
ever, during the domestication process and the spread
of agriculture from the Fertile Crescent, novel
adaptive traits suited for the new environments were
selected. One key event was the selection of spring
types that can be sown after winter. These spring
types lack the vernalization requirement and show a
different response to long days. Reduced photoperiod
response is important in Europe and North America,
where growing seasons are long (Turner et al. 2005).
Four heading date QTL located on four chromosomes
were identified (Table 1). The wild allele for the QTL
on 5A increases the value of heading date and so is
responsible for the late flowering of T. dicoccoides,
whereas the wild heading-date alleles on other
chromosomes can accelerate the flowering date (Peng
et al. 2003).
The evolution of spring types from a predomi-
nantly winter ancestral state is a key event in the
post-domestication spread of temperate cereals
(Cockram et al. 2007, 2009). On the basis of the
map positions, it can be postulated that the heading
date QTL on 5A (Fig. 4) may be similar to the
VRN1 gene mapped on chromosome 5A in T.
monococcum. This gene is similar to the Arabidop-
sis MADS-box transcription factor Apetala 1 (AP1),
which initiates the transition from the vegetative to
the reproductive state of the apical meristem (Yan
et al. 2003). The heading date QTL is located in a
collinear position with the photoperiod response
(Ppd) genes on the short arm of the group 2
chromosomes in wheat and barley. Major photope-
riod-related genes/gene families are conserved
between barley and Arabidopsis, involving the GI,
CO and FT genes in Arabidopsis and their orthologs
in barley HvGI, HvCO and HvFT (Griffiths et al.
2003; Dunford et al. 2005; Cockram et al. 2007;
Faure et al. 2007). However, these grass QTL did
not associate with flowering time but co-segregate
with orthologous Arabidopsis ‘‘flowering’’ genes.
Therefore, different major determinants of photope-
riod have been selected in the Triticeae (Borner
et al. 1998; Griffiths et al. 2003).
Grain yield and other traits
Primary domestication targets were likely the genes
that facilitated harvesting and enabled colonization of
new environments. Yield must have soon assumed
priority, minimizing labor input and land needs.
Using an advanced QTL mapping software, Multi-
QTL (http://www.multiqtl.com), eight yield QTL
located in five chromosomes were identified
(Table 1). The yield QTL overlapped with QTL for
other traits (Fig. 4). QTL conferring T. aestivum yield
traits were also mapped to chromosomes 3A, 4A and
5A (Shah et al. 1999; Campbell et al. 2003; Araki
et al. 1999; Kato et al. 2000).
During the domestication process involving the
qualitative and quantitative traits described above,
many other quantitative traits were also co-selected
by ancient farmers. These traits include plant height,
spike number/plant, spike weight/plant, single spike
weight, kernel number/plant, kernel number/spike,
kernel number/spikelet and spikelet number/spike.
Using MultiQTL mapping software, as many as 55
QTL effects were detected for these eight traits
(Table 1).
Plant height is an extremely important target trait
in modern wheat breeding since the ‘‘green revolu-
tion’’ in cereals was achieved by reducing plant
height, and thus the lodging susceptibility and
increase in grain yield (Hedden 2003). However,
dwarf wheat cultivars were used only in commercial
Fig. 4 Map and physical locations of DSFs and their involved
QTLs in L version maps of wild emmer wheat, T. dicoccoides.
Genetic map is on the left-hand side, and the right-hand side is
the physical bin map. Short arms of chromosomes are at the
top. The domestication syndrome factors and the correspond-
ing QTLs are shown on the right-hand side of the map: DSF,
domestication syndrome factor; KNS, kernel number/spike;
KNL, kernel number/spikelet; YLD, grain yield/plant; HT,
plant height; SLS, spikelet number/spike; SSW, single spike
weight; SWP, spike weight/plant; KNP, kernel number/plant;
HD, heading date; GWH, grain weight; SNP, spike number/
plant. The regular trait name represents a single QTL, the italic
trait name represents a single QTL (Q2) detected by linked-
QTL analysis, the regular trait name tailed with Q1 means the
1st QTL and tailed with Q2 means the 2nd QTL in a pair of
linked QTLs. A (5) tailed a trait name means that the QTL
effect is not significant at the level of 5% of FDR but is
significant at the FDR=10%, whereas (10) means that the effect
is not significant on the FDR=10%. (Reproduced from Peng
et al. 2003)
c
290 Mol Breeding (2011) 28:281–301
123
Mol Breeding (2011) 28:281–301 291
123
Fig. 4 continued
292 Mol Breeding (2011) 28:281–301
123
production after the 1960 s, and most of the wheat
landraces are tall. Therefore, ancient farmers did not
select the dwarf but selected the tall mutants that had
higher biomass and yielding potential during domes-
tication. Four QTL or two pairs of linked QTL for
plant height were detected in chromosomes 5A and
7B (Table 1). One of the T. dicoccoides alleles on
chromosome 5A was able to reduce plant height by
9.6–15.2 cm (Peng et al. 2003).
Spike number is one of the most important yield
components and is highly correlated with tillering
capacity in wheat. The grassy wild wheat, e.g., T.
dicoccoides, usually has strong tillering ability and
can be used as a source to increase the tillering
capacity or spike number of wheat cultivars. Seven
QTL effects for spike number were detected in five
chromosomes (Table 1). A single recessive gene (tin)
located on chromosome 1AS was found to control
tiller number (Spielmeyer and Richards 2004). This
gene is perhaps a homeologous allele of the striking
spike number QTL on chromosome 1B of T.
dicoccoides (Peng et al. 2003). Comparative genom-
ics analyses revealed that tin, rice reduced tillering
mutations, and the barley uniculm2 mutant map to
nonsyntenic chromosomes (Rossini et al. 2006).
Recently, a tiller inhibition gene tin3 was identified
and mapped to the long arm of T. monococcum
chromosome 3Am (Kuraparthy et al. 2007, 2008).
Spike weight/plant and single spike weight are
significantly correlated with each other, and also with
grain weight/size and yield (Peng et al. 2003). Ten
QTL effects were detected for spike weight/plant in
six chromosomes, and five QTL effects were detected
for single spike weight in four chromosomes
(Table 1). Kernel number/plant, kernel number/spike,
kernel number/spikelet and spikelet number/spike are
highly correlated with each other and also with yield
(Peng et al. 2003). Nine, seven, seven and six QTL
effects were identified for kernel number/plant,
kernel number/spike, kernel number/spikelet and
spikelet number/spike, respectively (Table 1).
Among the chromosomes carrying domestication
QTL, 5A harbours QTL effects for all the 11 traits
examined, 2A carries QTL effects for 10 of the 11
traits, and 1B has QTL effects for 9 of the 11 traits
(Table 1). Therefore, chromosomes 5A, 2A and 1B
played key roles in domestication modification of
these quantitative traits. Interestingly, the free-thresh-
ing gene Q discussed above is located in chromosome
5A (Luo et al. 2000). It is thus highly possible that the
key domestication gene, Q, has pleiotropic effects on
yield and yield components (Kato et al. 2003).
Domestication syndrome factors involving
quantitative traits and gene-rich regions
Domesticated species differ from their wild ancestors
and relatives in a set of traits that is known as the
domestication syndrome. The most important syn-
drome traits include growth habit, flowering time,
seed dispersal and gigantism (Frary and Doganlar
2003). It would be very helpful for wheat breeding
for high yield and good adaptability to understand the
genomics/genetics of syndrome traits (Killian et al.
2009). Most of the significant QTL for domestica-
tion-related traits are clustered mainly in a limited
number of intervals in chromosomes 1B, 2A, 3A and
5A (Fig. 4). Consequently, the total number of
intervals carrying domestication QTL is only 16,
though as many as 70 QTL effects were detected. The
chromosomal regions harboring a cluster of domes-
tication QTL are referred to as domestication syn-
drome factors (DSFs). Only seven DSFs, each
involving a pleiotropic QTL or cluster of QTLs
affecting 5–11 traits, were found in four chromo-
somes in wild emmer wheat (Fig. 4). Although most
domestication traits are quantitatively inherited, the
dramatic morphological changes that accompanied
domestication may be due to relatively few genes
(Frary and Doganlar 2003). This limited number of
DSFs of wheat (Fig. 4) corroborates the results in
other cereal crops, showing that the domestication
syndrome is under a relatively simple and rapidly
evolving genetic control (Paterson et al. 1995).
Gene distribution in Triticeae chromosomes is
highly nonrandom, with a few gene-rich regions
alternating with gene-poor regions, as in other
eukaryotes. Gene-rich regions correspond to hot spots
of recombination (Gill et al. 1996a, b; Kunzel et al.
2000; Peng et al. 2004). The map positions of all
seven wheat DSFs appear to overlap with gene-rich
regions (Fig. 4) and the key domestication gene,
Q. Therefore, the high pleiotropy and/or tight linkage
of most wheat domestication QTL suggest an impor-
tant role for recombination both in consolidation of
positive mutations within the DSF clusters (Otto and
Barton 1997) and in reducing the antagonism between
Mol Breeding (2011) 28:281–301 293
123
artificial and background (purifying) selection (Rice
2002). The presumed coincidence between DSFs and
gene-rich regions could facilitate component dissec-
tion of these factors, their further fine mapping, and
finally map-based cloning. Dvorak (2009), however,
pointed out that the evidence for gene-rich islands is
weak. He proposed a model accounting for correlation
between gene flow density and recombination rate.
Furthermore, he also suggested that the vast numbers
of repeated sequences in the Triticeae genomes (90%
of the nuclear genomes) play a role in the evolution of
new genes and in adaptation. The dramatic dynamics
and evolution of adaptation and speciation of trans-
posable elements (TEs) in diploid wheat has been
described by Belyayev et al. (2010), and generally in
Triticeae by Sabot and Schulman (2009).
Role of A and B genomes in wheat domestication
Inter-parental PstI-based amplified fragment length
polymorphisms (AFLPs) showed that molecular
markers are nonrandomly distributed among the A
and the B genomes of tetraploid wheat: 60% of
polymorphic AFLP loci were mapped to the B
genome (Peng et al. 2000). Likewise, higher poly-
morphism in the B than in the A genome applies to
microsatellites (Roder et al. 1998) and restriction
fragment length polymorphism markers (Liu and
Tsunewaki 1991) in common hexaploid wheat as well
as in T. dicoccoides in Israel (Li et al. 2000).
However, in our wild wheat domestication QTL
mapping study, the numbers of both QTL effects and
domestication syndrome factors in the A genome
significantly exceeded those in the B genome (Peng
et al. 2003). The key domestication genes, sos and Q,
are also located in A chromosomes (Luo et al. 2000;
Sood et al. 2009). Therefore, the wheat A genome
may have played a more important role than the B
genome in the wheat domestication process. Gupta
et al. (2008) believed that diploid wheat carrying the
A genome was the first wheat to be domesticated, so
that most of the domestication-related traits in
different wheats must have been selected within the
A genome. However, domestication is assumed to
have occurred independently on tetraploid and dip-
loid wild wheats. Therefore extensive and intensive
phylogenetic analyses are needed to explain the fact
that the A genome has played a stronger role than the
B genome in the domestication process.
Importance of Triticum dicoccoides in wheat
domestication and breeding
As reviewed above, hexaploid bread wheat is derived
from a spontaneous hybridization between tetraploid
wheat and the diploid D genome donor, Ae. tauchii.
The wheat domestication events mainly occurred in
diploid wheat (T. boeoticum) containing AmAm and
tetraploid wheat (T. dicoccoides) containing AuAuBB
genomes. The Au genome in bread and durum wheat
is different from Am in T. boeoticum but the same as
in T. dicoccoides. Therefore, the wild emmer wheat,
T. dicoccoides, actually is central to wheat domesti-
cation evolution (Zohary and Hopf 2000; Nevo et al.
2002; Nevo 2011). Dvorak et al. (2006) conducted a
deliberately designed analysis of genetics and genom-
ics of wheat domestication, and showed for the first
time that wild tetraploid wheat participated in the
evolution of hexaploid wheat.
T. dicoccoides possesses important beneficial
traits, e.g., resistance to stripe rust, stem rust,
powdery mildew and soil born wheat mosaic virus,
amino acid composition, grain protein content and
storage protein genes (HMW glutenins), high photo-
synthetic yield, salt and drought tolerance, herbicide
resistance, amylases and alpha amylase inhibitors,
micronutrients such as Zn and Fe (Cakmak et al.
2004; Uauy et al. 2006), and genotypic variation for
diverse traits such as biomass, earliness, nitrogen
content, yield, short stature and high tillering capacity
(Nevo et al. 2002). However, T. dicoccoides also
shows agriculturally deleterious features such as
brittle rachis; no-free-threshing characteristic; few,
small and light spikes; and small grains. Neverthe-
less, among the 75 domestication QTL effects for 11
traits, wild QTL alleles of T. dicoccoides for 18
(24%) effects were agriculturally beneficial: e.g.,
contributing to short plant, early heading date, higher
spike number/plant, higher spike weight/plant, higher
kernel number per spikelet, higher GWH and higher
yield (Peng et al. 2003). Thus, this large portion of
cryptic beneficial alleles, together with genes for
resistance or tolerance to biotic and abiotic stresses
and high protein content (Nevo et al. 2002), could
294 Mol Breeding (2011) 28:281–301
123
substantially advance the utilization of T. dicoccoides
for wheat improvement (Xie and Nevo 2008; Gus-
tafson et al. 2009; Nevo and Chen 2010, Nevo 2011).
To date, much of the vast potential adaptive genetic
resources existing in wild emmer remains to be
tapped and exploited for wheat improvement.
Conclusions and prospects
Wheat is one of the most important grain crops in the
world. T. dicoccoides, the progenitor of cultivated
wheats, is central to wheat domestication, fitting the
gradual and multi-site model rather than the fast and
single-site model. Domestication has genetically not
only transformed the brittle rachis, tenacious glume
and non-free threshability, but also modified yield and
yield components in wheat. Wheat domestication is
actually restricted to a limited number of chromosome
regions, or domestication syndrome factors. This
finding is helpful for studies on genetics and genomics
of wheat domestication. The physical mapping of
polyploidy plant species (Fleury et al. 2010; Luo et al.
2010) and sequencing of the wheat genome initiated by
the International Wheat Genome Sequencing Consor-
tium (IWGSC) (Feuillet and Eversole 2007; Feuillet
and Muehlbauer 2009) will further accelerate genomic
studies on wheat domestication by providing powerful
genomics tools. During agricultural development,
early domesticates were gradually replaced first by
landraces and traditional varieties, and later by genet-
ically less diverse modern cultivars. This has resulted
in genetic bottlenecks and loss of diversity in breeding
germplasm (Tanksley and McCouch 1997; Nevo 2004;
Fu and Somers 2009). Though experiencing diversity
bottlenecks, wheat has strong adaptability to diverse
environments and end uses due to the adaptive
complexes that evolved in wild emmer in the near
Fertile Crescent (Nevo et al. 2002). Wheat compen-
sates for these bottlenecks by capturing part of the
genetic diversity of its progenitors and by generating
new diversity at a relatively fast pace (Dubcovsky and
Dvorak 2007). Therefore, germplasm collections are
essential to conserve biodiversity and thus pay big
dividends to agriculture when used efficiently (Nevo
2007, 2009, 2011; Nevo et al. 2002; Xie and Nevo
2008; Nevo and Chen 2010; Johnson 2008).
As a wheat progenitor, wild emmer wheat should be
subjected to in-depth studies to evaluate the structural,
functional and regulatory polymorphisms adapting it
to environmental stresses (Nevo 2004; Parsons 2005).
The available crop genome sequences and the current
sequencing of the wheat genome can transform today’s
biology (Schuster 2008), dramatically advancing both
the theory and application of wheat domestication
studies. The relationship between genomic and epige-
nomic diversities (Kashkush et al. 2002; Levy and
Feldman 2004; Kashkush 2007) could be highlighted
by deciphering the regulatory function of noncoding
genomes on genic components (Li et al. 2002, 2003,
2004). Regulation in particular might be the key in
future domestication studies. It might decipher both
speciation and adaptation processes to stressful, het-
erogeneous and changing environments. The non-
random adaptive processes and complexes in wild
emmer and other wheat relatives could provide the
basis for wheat improvement such as single genes,
QTL and interacting biochemical networks.
It is essential to follow domestication processes
and unravel many functional and regulatory genes
that were eliminated from the cultivars during
domestication, primarily by modern breeding. Iden-
tifying the polycentric sites of wild emmer domes-
tication in the southern Levant versus monocentric
ideas is feasible by tracking non-brittle rachis
remains during initial phases of the ‘‘agricultural
revolution’’, which may have been a gradual rather
than a revolutionary process. This future research
could identify adaptive genes lost during domestica-
tion and enable their active introgression from wild
emmer back to cultivated wheat for genetic rein-
forcement (Nevo 2011).
Whole genomes of several crops including rice,
maize and sorghum have been sequenced, and the
sequences have proved to be useful in domestication
genomics studies (Dvorak 2009). The sequence data
can be used to study the origin of genes and gene
families, track rates of sequence divergence over time,
and provide hints about how genes evolve and generate
products with novel biological properties (Hancock
2005, Feuillet and Muehlbauer 2009). However, wheat
genome sequencing is still in its infancy due to its huge
genome size and the huge proportion of repetitive
sequences (Dvorak 2009). Nevertheless, physical
mapping and sequencing of the wheat genome (Feu-
illet and Eversole 2007) have been conducted by the
IWGSC and other research institutions since 2005.
Physical maps (Korol et al. 2009; Fleury et al. 2010;
Mol Breeding (2011) 28:281–301 295
123
Luo et al. 2010) are mandatory for the development of
whole genome reference sequences of large and
complex genomes, such as those of the Triticeae crop
species wheat, barley and rye (Stein 2009). A bacterial
artificial chromosome (BAC)-based integrated physi-
cal map of the largest wheat chromosome 3B
(995 Mb) was constructed recently (Paux et al.
2008). This physical map establishes a template for
the remaining wheat chromosomes and demonstrates
the feasibility of constructing physical maps in large,
complex, polyploid genomes using a chromosome-
based approach. These efforts develop the needed
background and tools for sequencing the hexaploid
and diploid wheat genomes and provide theoretical
evolutionary perspectives and excellent tools for
unfolding wheat domestication studies and for opti-
mizing breeding practices (Feuillet and Eversole
2007). This is a long-term, milestone-based strategy
that delivers products and tools while working towards
crop improvement, both qualitatively and quantita-
tively. Upon completion of genome sequencing of
either diploid wild wheat, T. urartu or Ae. tauschii, or
hexaploid bread wheat, domestication syndrome fac-
tors and other relevant genes and QTL could be
isolated, and effects of wheat domestication could be
accurately estimated. The improvement of bread
wheat is a future challenge for mankind, based on
the evidence and ideas presented above and presented
much earlier by Aaronsohn (Aaronsohn and Schwein-
furth 1906; Aaronsohn 1910), and based on the distinct
adaptive complexes of T. dicoccoides to environmen-
tal stress and their direct relevance to wheat domes-
tication (Nevo et al. 2002).
Acknowledgments This work was supported in part by the
China National Science Foundation Grant Nos. 31030055 &
30870233, Chinese Academy of Sciences under the Important
Directional Program of Knowledge Innovation Project Grant
No. KSCX2-YW-Z-0722, the CAS Strategic Priority Research
Program Grant No. XDA05130403, the ‘‘973’’ National Key
Basic Research Program Grant No. 2009CB118300, and the
Ancell Teicher Research Foundation for Genetics and Molecular
Evolution.
References
Aaronsohn A (1910) Agricultural and botanical explorations in
Palestine. Bureau of Plant Industry Bull 80, USDA, No 180
Aaronsohn A, Schweinfurth G (1906) Die Auffindung des
wilden Emmers (Triticum dicoccum) in Nordpalastina.
Altneuland Monatsschrift fur die irtschaft. Erschliessung
Palastinas 7–8:213–220
Akhunov ED, Akhunova AR, Anderson OD, Anderson JA,
Blake N, Clegg MT, Coleman-Derr D, Conley EJ,
Crossman CC, Deal KR, Dubcovsky J, Gill BS, Gu YQ,
Hadam J, Heo H, Huo N, Lazo GR, Luo MC, Ma YQ,
Matthews DE, McGuire PE, Morrell PL, Qualset CO,
Renfro J, Tabanao D, Talbert LE, Tian C, Toleno DM,
Warburton ML, You FM, Zhang W, Dvorak J (2010)
Nucleotide diversity maps reveal variation in diversity
among wheat genomes and chromosomes. BMC
Genomics 11:702
Allaby RG (2010) Integrating the processes in the evolutionary
system of domestication. J Exp Bot 61:935–944
Araki E, Miura H, Sawada S (1999) Identification of genetic
loci affecting amylose content and agronomic traits on
chromosome 4A of wheat. Theor Appl Genet 98:977–984
Balter M (2007) Seeking agriculture’s ancient roots. Science
316:1830–1835
Belyayev A, Kalendar R, Brodsky L, Nevo E, Schulman AH,
Raskina O (2010) Transposable elements in a marginal
plant population: temporal fluctuations provide new
insights into genome evolution of wild diploid wheat.
Mobile DNA 1:6
Bennett MD, Leitch IJ (2010) Plant DNA C-values database
(release 5.0, Dec. 2010). http://www.kew.org/cvalues/
Borner A, Korzun V, Worland AJ (1998) Comparative genetic
mapping of loci affecting plant height and development in
cereals. Euphytica 100:245–248
Brown AHD (2010) Variation under domestication in plants:
1859 and today. Phil Trans R Soc B 365:2523–2530
Buckler ES, Thornsberry JM, Kresovich S (2001) Molecular
diversity, structure and domestication of grasses. Genet
Res 77:213–218
Cakmak IA, Torun E, Millet E, Feldman M, Fahima T, Korol
AB, Nervo E, Braun HJ, Ozkan H (2004) Triticum dic-occoides: an important genetic resource for increasing
zinc and iron concentration in modern cultivated wheat.
Soil Sci Plant Nutr 50:1047–1054
Campbell B, Baenziger PS, Gill KS, Eskridge KM, Budak H,
Erayman M, Dweikat I, Yen Y (2003) Identification of
QTLs and environmental interactions associated with
agronomic traits on chromosome 3A of wheat. Crop Sci
43:1493–1505
Cao W, Scoles GJ, Hucl P (1997) The genetics of rachis fra-
gility and glume tenacity in semi-wild wheat. Euphytica
94:119–124
Carver BF (2009) Wheat science and trade. Wiley, Danvers,
p 569
Chao S, Dubcovsky J, Dvorak J, Luo MC, Baenziger SP,
Matnyazov R, Clark DR, Talbert LE, Anderson JA, Dre-
isigacker S, Glover K, Chen J, Campbell K, Bruckner PL,
Rudd JC, Haley SD, Carver BF, Perry S, Sorrells ME,
Akhunov ED (2010) Population- and genome-specific
patterns of linkage disequilibrium and SNP variation in
spring and winter wheat (Triticum aestivum L.). BMC
Genomics 11:727
Chen QF, Yen C, Yang JL (1998) Chromosome location of the
gene for brittle rachis in the Tibetan weedrace of common
wheat. Genet Res Crop Evol 45:21–25
296 Mol Breeding (2011) 28:281–301
123
Cockram J, Jones H, Leigh FJ, O’Sullivan D, Powell W, Laurie
DA, Greenland AJ (2007) Control of flowering time in
temperate cereals: genes, domestication, and sustainable
productivity. J Exper Bot 58:1231–1244
Cockram J, Norris C, O’Sullivan DM (2009) PCR-based
markers diagnostic for Spring and Winter seasonal growth
habit in barley. Crop Sci 49:403–410
Damania AB (1998) Diversity of major cultivated plants
domesticated in the Near East. In: Damania AB, Valkoun
J, Willcox G, Qualset CO (eds) The origins of agriculture
and crop domestication. Proceedings of the Harlan Sym-
posium. ICARDA, Aleppo, pp 51–64
Darwin C (1905) The variation of animals and plants under
domestication. John Murray, London (popular edition in
two volumes) 566 p
Doebley J (1989) Isozymic evidence and the evolution of crop
plants. In: Soltis D, Soltis P (eds) Isozymes in Plant
Biology. Dioscorides Press, Portland, pp 165–191
Doebley JF, Gaut BS, Smith BD (2006) The molecular genetics
of crop domestication. Cell 127:1309–1321
Dorofeev VF, Filatenko AA, Migushova EF, Udaczin RA, Ja-
kubziner MM (1979) Wheat. In: Dorofeev VF, Korovina ON
(eds) Flora of Cultivated Plants, vol 1. Leningrad, Russia
Dubcovsky J, Dvorak J (2007) Genome plasticity a key factor
in the success of polyploid wheat under domestication.
Science 316:1862–1866
Dunford RP, Griffiths S, Christodoulou V, Laurie DA (2005)
Characterisation of a barley (Hordeum vulgare L.)
homologue of the Arabidopsis flowering time regulator
GIGANTEA. Theor Appl Genet 110:925–931
Dvorak J (2009) Triticeae genome structure and evolution. In:
Feuiller C, Muehlbauer GJ (eds) Genetics and genomics
of the Triticeae, plant genetics and genomics: crops and
models 7. Springer, Berlin, pp 685–711
Dvorak J, Akhunov E (2005) Tempos of gene locus deletions
and duplications and their relationship to recombination
rate during diploid and polyploid evolution in the Aegi-lops-Triticum alliance. Genetics 17:323–332
Dvorak J, Diterlizzi P, Zhang HB, Resta P (1993) The evolu-
tion of polyploidy wheats: identification of the A genome
donor species. Genome 36:21–31
Dvorak J, Luo MC, Yang ZL (1998) Genetic evidence on the
origin of Triticum aestivum L. In: Damania AB, Valkoun
J, Willcox G, Qualset CO (eds) The origins of agriculture
and crop domestication. Proceedings of the Harlan sym-
posium. ICARDA, Aleppo, pp 235–251
Dvorak J, Akhunov ED, Akhunov AR, Deal KR, Luo MC
(2006) Molecular characterization of a diagnostic DNA
marker for domesticated tetraploid wheat provides evi-
dence for gene flow from wild tetraploid wheat to hexa-
ploid wheat. Mol Biol Evol 23:1386–1396
Dvorak J, Luo MC, Akhunov ED (2011) N.I. Vavilov’s theory
of centers of diversity in light of current understanding of
wheat diversity, domestication and evolution. Czech J
Genet Plant Breed (in press)
Elias EM, Steiger KD, Cantrell RG (1996) Evaluation of lines
derived from wild emmer chromosome substitutions II.
Agronomic traits. Crop Sci 36:228–233
Faris J, Gill BS (2002) Genomic targeting and high resolution
mapping of the domestication gene Q in wheat. Genome
45:706–718
Faris JD, Fellers JP, Brooks SA, Gill BS (2003) A bacterial
artificial chromosome contig spanning the major domes-
tication locus Q in wheat and identification of a candidate
gene. Genetics 164:311–321
Faris JD, Simons KJ, Zhang Z, Gill B (2005) The wheat super
domestication gene Q. Front Wheat Biosci 100:129–148
Faure S, Higgins J, Turner A, Laurie DA (2007) The FLOW-
ERING LOCUS T-like gene family in barley (Hordeumvulgare). Genetics 176:599–609
Feldman M, Kislev ME (2007) Domestication of emmer wheat
and evolution of free-threshing tetraploid wheat. Israel J
Plant Sci 55:207–221
Feldman M, Sears ER (1981) The wild gene resources of
wheat. Sci Am 244:102–112
Feldman M, Lupton FGH, Miller TE (1995) Wheats. Triticumspp. (Gramineae- Triticinae). In: Smartt J, Simmonds NW
(eds) Evolution of crop plants. Longman Scientific &
Technical Press, London, pp 84–192
Feuillet C, Eversole K (2007) Physical mapping of the wheat
genome: a coordinated effort to lay the foundation for
genome sequencing and develop tools for breeders. Isr J
Plant Sci 55:307–313
Feuillet C, Muehlbauer GJ (2009) Genetics and genomics of
the Triticeae, plant genetics and genomics: crops and
models 7. Springer, Berlin
Fleury D, Luo MC, Dvorak J, Ramsay L, Gill BS, Anderson
OD, You FM, Shoaei Z, Deal KR, Langridge P (2010)
Physical mapping of a large plant genome using global
high-information-content-fingerprinting: the distal region
of the wheat ancestor Aegilops tauschii chromosome 3DS.
BMC Genomics 11:382
Frary A, Doganlar S (2003) Comparative genetics of crop
plant domestication and evolution. Turk J Agric Forest
27:59–69
Fu YB, Somers DJ (2009) Genome-wide reduction of genetic
diversity in wheat breeding. Crop Sci 49:61–168
Fuller DQ (2007) Contrasting patterns in crop domestication
and domestication rates: recent archaeobotanical insights
from the Old World. Ann Bot 100:903–924
Fuller DQ, Allaby RG, Stevens C (2010) Domestication as
innovation: the entanglement of techniques, technology
and chance in the domestication of cereal crops. World
Archaeol 42:13–28
Gandilian PA (1972) On wild growing Triticum species of
Armenian SSR. Bot Zhur 57:173–181
Gegas VC, Nazari A, Griffiths S, Simmonds J, Fish L, Orford
S, Sayers L, Doonan JH, Snape JW (2010) A genetic
framework for grain size and shape variation in wheat.
Plant Cell 22:1046–1056
Gepts P (2004) Crop domestication as a long-term selection
experiment. Plant Breed Rev 24:1–44
Giles RJ, Brown TA (2006) GluDy allele variations in Aegilopstauschii and Triticum aestivum: implications for the ori-
gins of hexaploid wheats. Theor Appl Genet 112:
1563–1572
Gill KS, Gill BS, Endo TR, Boyko EV (1996a) Identification
and high-density mapping of gene-rich regions in chromo
some group 5 of wheat. Genetics 143:1001–1012
Gill KS, Gill BS, Endo TR, Taylor T (1996b) Identification and
high-density mapping of gene-rich regions in chromo-
some 1 of wheat. Genetics 144:1883–1891
Mol Breeding (2011) 28:281–301 297
123
Gill BS, Friebe B, Raupp WJ, Wilson DL, Cox TS, Sears RG,
Brown-Guedira GL, Fritz AK (2006) Wheat genetics
resource center: the first 25 years. Adv Agron 89:73–136
Gill BS, Li W, Sood S, Kuraparthy V, Friebe Simons KJ,
Zhang Z, Faris JD (2007) Genetics and genomics of wheat
domestication-driven evolution. Isr J Plant Sci 55:
223–229
Griffiths S, Dunford RP, Coupland G, Laurie DA (2003) The
evolution of CONSTANS-like gene families in barley,
rice and Arabidopsis. Plant Physiol 131:1855–1867
Gupta PK, Mir RR, Mohan A, Kumar J (2008) Wheat
genomics: present status and future prospects. Intl J Plant
Genomics, vol 2008, Article ID 896451, 36 pages. doi:
10.1155/2008/896451
Gustafson P, Raskina O, Ma X, Nevo E (2009) Wheat evolu-
tion, domestication, and improvement. In: Carver BF (ed)
Wheat: science and trade. Wiley, Danvers, pp 5–30
Hancock JF (2005) Contributions of domesticated plant studies
to our understanding of plant evolution. Ann Bot 96:
953–963
Harlan JR (1992) Crop and man. American Society of
Agronomy, Crop Science Society of America, Madison
Haudry A, Cenci A, Ravel C, Bataillon T, Brunel D, Poncet C,
Hochu I, Poirier S, Santoni S, Gle0min S, David J (2007)
Grinding up wheat: a massive loss of nucleotide diversity
since domestication. Mol Biol Evol 24:1506–1517
Hedden P (2003) The genes of the green revolution. Trends
Genet 19:5–9
Heun M, Schafer-Pregl R, Klawan D, Castagna R, Accerbi M,
Borghi B, Salamini F (1997) Site of einkorn wheat
domestication identified by DNA fingerprinting. Science
278:1312–1314
Hillman G, Davies S (1990) Measured domestication rates in
wild wheats and barley under primitive cultivation, and
their archaeological implications. J World Prehistory
4:157–222
Honne BI, Heun M (2009) On the domestication genetics of
self-fertilizing plants. Veget Hist Archaeobot 18:269–272
Huang S, Sirikhachornkit A, Su X, Faris J, Gill B, Haselkorn R,
Gornicki P (2002) Genes encoding plastid acetyl-CoA
carboxylase and 3-phosphoglycerate kinase of the Triti-cum/Aegilops complex and the evolutionary history of
polypoid wheat. Proc Natl Acad Sci USA 99:8133–8138
Inda LA, Segarra-Moragues Jose Gabriel, Muller Jochen,
Peterson Paul M, Catalan Pilar (2008) Dated historical
biogeography of the temperate LoHinae (Poaceae, Pooi-
deae) grasses in the northern and southern hemispheres.
Mol Phylogenet Evol 46:932–957
Jantasuriyarat C, Vales MI, Watson CJW, Riera-Lizarazu O
(2004) Identification and mapping of genetic loci affect-
ing the free-threshing habit and spike compactness in
wheat (Triticum aestivum L.). Theor Appl Genet 108:
261–273
Johnson BL (1975) Identification of the apparent B-genome
donor of wheat. Can J Genet Cytol 17:21–39
Johnson RC (2008) Gene banks pay big dividends to agricul-
ture, the environment, and human welfare. PLoS Biol
6(6):e148. doi:10.1371/journal.pbio.0060148
Johnson BL, Dhaliwal HS (1976) Reproductive isolation of
Triticum boeticum and Triticum urartu and the origin of
the tetraploid wheats. Am J Bot 63:1088–1094
Kashkush K (2007) Genome-wide impact of transcriptional
activation of long terminal repeat retrotransposons on the
expression of adjacent host genes. Isr J Plant Sci 55:
241–250
Kashkush K, Feldman M, Levy AA (2002) Gene loss, silencing
and activation in a newly synthesized wheat allotetraploid.
Genetics 160:1651–1656
Kato K, Miura H, Akiyama M, Kuroshima M, Sawada S (1998)
RFLP mapping of the three major genes, Vrn1, Q and B1,
on the long arm of chromosome 5A of wheat. Euphytica
101:91–95
Kato K, Miura H, Sawada S (2000) Mapping QTLs controlling
grain yield and its components on chromosome 5A of
wheat. Theor Appl Genet 101:933–943
Kato K, Sonokawa R, Miura H, Sawada S (2003) Dwarfing
effect associated with the threshability gene Q on wheat
chromosome 5A. Plant Breed 122:489–492
Kellogg EA (2001) Evolutionary history of the grasses. Plant
Physiol 125:1198–1205
Kerber ER (1964) Wheat: reconstitution of the tetraploid
component (AABB) of hexaploids. Science 143:
253–255
Kerber RE, Rowland GG (1974) Origin of the threshing
character in hexaploid wheat. Can J Genet Cytol 16:
145–154
Kihara H (1944) Discovery of the DD-analyser, one of the
ancestors of Triticum vulgare. Agric Hortic (Tokyo) 19:
13–14
Kilian B, Ozkan H, Walther A, Kohl J, Dagan T, Salamini F,
Martin W (2007) Molecular diversity at 18 loci in 321
wild and 92 domesticate lines reveal no reduction of
nucleotide diversity during Triticum monococcum (ein-
korn) domestication: Implications for the origin of agri-
culture. Mol Biol Evol 24:2657–2668
Kilian B, Ozkan H, Pozzi C, Salamini F (2009) Domestication
of the Triticeae in the Fertile Crescent. In: Feuillet C,
Muehlbauer GJ (eds) Genetics and genomics of the Tri-
ticeae, plant genetics and genomics: crops and models 7.
Springer, Berlin, pp 81–119
Kislev ME (1980) Triticum parvicoccum sp. nov., the oldest
naked wheat. Israel J Bot 28:95–107
Kislev ME, Nadel D, Carmi I (1992) Epipalaeolithic
(19,000 BP) cereal and fruit diet at Ohalo II, Sea of
Galilee, Israel. Rev Palaeobot Palynol 73:161–166
Konishi S, Izawa T, Lin SY, Ebana K, Fukuta Y, Sasaki T,
Yano M (2006) An SNP caused loss of seed shattering
during rice domestication. Science 312:1392–1396
Korol A, Mester D, Frenkel Z, Ronin Y (2009) Methods of
genetic analysis in the Triticeae. In: Feuillett C, Mu-
elbauer GJ (eds) Genetics and genomics of the Triticeae,
plant genetics and genomics: crops and models 7.
Springer, Berlin, pp 163–199
Kuckuck H (1959) Neuere Arbeiten zur Entstehung der hexa-
ploiden Kulturweizen. Z. Pflanzenzuchtg. 41:205–226
Kunzel G, Korzum L, Meister A (2000) Cytologically inte-
grated physical restriction fragment length polymorphism
maps for the barley genome based on translocation
breakpoints. Genetics 154:397–412
Kuraparthy V, Sood S, Chunneja P, Dhaliwal HS, Gill BS
(2007) Identification and mapping of tiller inhibition gene
(tin3) in wheat. Theor Appl Genet 114:285–294
298 Mol Breeding (2011) 28:281–301
123
Kuraparthy V, Sood S, Gill BS (2008) Genomic targeting and
mapping of tiller inhibition gene (tin3) of wheat using
ESTs and synteny with rice. Funct Integr Genomics
8:33–42
Levy AA, Feldman M (2004) Genetic and epigenetic repro-
gramming of the wheat genome upon allopolyploidiza-
tion. Biol J Linn Soc 82:607–613
Li W, Gill BS (2006) Multiple genetic pathways for seed
shattering in the grasses. Func Integr Genomics 6:
300–309
Li YC, Fahima T, Korol AB, Peng J, Roder MS, Kirzhner VM,
Beiles A, Nevo E (2000) Microsatellite diversity corre-
lated with ecological-edaphic and genetic factors in three
microsites of wild emmer wheat in North Israel. Mol Biol
Evol 17:851–862
Li YC, Korol AB, Fahima T, Beiles A, Nevo E (2002)
Microsatellites: genomic distribution, putative functions
and mutational mechanisms: a review. Mol Ecol 11:
2453–2465
Li YC, Fahima T, Roder MS, Kirzhner VM, Beiles A, Korol
AB, Nevo E (2003) Genetic effects on microsatellite
diversity in wild emmer wheat (Triticum dicoccoides) at
the Yehudiyya microsite, Israel. Heredity 90:156–160
Li YC, Korol AB, Fahima T, Nevo E (2004) Microsatellites
within genes: structure, function and evolution. Mol Biol
Evol 21:991–1007
Liu YG, Tsunewaki K (1991) Restriction fragment length
polymorphism analysis of wheat. II. Linkage maps of the
RFLP sites in common wheat. Jpn J Genet 66:617–633
Luo MC, Yang ZL, Dvorak J (2000) The Q locus of Iranian and
European spelt wheat. Theor Appl Genet 100:602–606
Luo MC, Yang ZL, You FM, Kawahara T, Waines JG, Dvorak
J (2007) The structure of wild and domesticated emmer
wheat populations, gene flow between them, and the site
of emmer domestication. Theor Appl Genet 114:947–959
Luo MC, Deal KR, Akhunov ED, Akhunova AR, Anderson
OD, Anderson JA, Blake N, Clegg MT, Coleman-Derr D,
Conley EJ, Crossman CC, Dubcovsky J, Gill BS, Gu YQ,
Hadam J, Heo HY, Huo N, Lazo G, Ma Y, Matthews DE,
McGuire PE, Morrell PL, Qualset CO, Renfro J, Tabanao
D, Talbert LE, Tian C, Toleno DM, Warburton ML, You
FM, Zhang W, Dvorak J (2009) Genome comparisons
reveal a dominant mechanism of chromosome number
reduction in grasses and accelerated genome evolution in
Triticeae. Proc Natl Acad Sci USA 106:15780–15785
Luo MC, Ma Y, You FM, Anderson OD, Kopecky D, Simkova
H, Safar J, Dolezel J, Gill BS, McGuire PE, Dvorak J
(2010) Feasibility of physical map construction from
fingerprinted bacterial artificial chromosome libraries of
polyploid plant species. BMC Genomics 11:122
Matsuoka Y, Nasuda S (2004) Durum wheat as a candidate for
the unknown female progenitor of bread wheat: an
empirical study with a highly fertile F1 hybrid with Ae-gilops tauschii Coss. Theor Appl Genet 109:1710–1717
McFadden ES, Sears ER (1946) The origin of Triticum speltaand its free-threshing hexaploid relatives. J Hered
37(81–89):107–116
McKey J (1966) Species relationships in Triticum. Hereditas
2:237–276
Mori N, Ishii T, Ishido T, Hirosawa S, Watatani H, Kawahara T,
Nesbitt M, Belay G, Takumi S, Ogihara Y, Nakamura C
(2003) Origin of domesticated emmer and common wheat
inferred from chloroplast DNA fingerprinting. 10th inter-
national wheat genetics symposium. Paestum, pp 25–28
Muramatsu M (1963) Dosage effect of the spelta gene q of
hexaploid wheat. Genetics 48:469–482
Nalam V, Vales MI, Watson CJW, Kianian SF, Riera-Lizarazu
O (2006) Map based analysis of genes affecting the brittle
rachis character in tetraploid wheat (Triticum turgidum).
Theor Appl Genet 112:373–381
Nalam V, Vales MI, Watson CJW, Johnson EB, Riera-Lizarazu
O (2007) Map based analysis of genetic loci on chromo-
some 2D that affect glume tenacity and threshability,
components of the free-threshing habit in common wheat
(Triticum aestivum L.). Theor Appl Genet 116:135–145
Nesbitt M, Samuel D (1996) From stable crop to extinction?
The archaeology and history of the hulled wheats. In:
Padulosi S, Hammer K, Heller J (eds) hulled wheats.
International Plant Genetic Resources Institute, Rome,
pp 41–100
Nevo E (2004) Genomic diversity in nature and domestication.
In: Henry R (ed) Diversity and evolution of plants.
Genotypic and phenotypic variation in higher plants.
CABI Publishing CAB International, Wallingford,
pp 287–315
Nevo E (2007) Evolution of wild wheat and barley and crop
improvement: studies at the Institute of Evolution. Isr J
Plant Sci 55:251–263
Nevo E (2009) Ecological genomics of natural plant popula-
tions: the Israeli perspective. In: Somers DJ, Langridge P,
Gustafson JP (eds) Methods in molecular biology, plant
genomics, vol 513. Human Press, A part of Springer
Science ? Business Media, pp 321–344
Nevo E (2011) Triticum. In: Kole C (ed) Wild crop relatives:
genomic and breeding resources, cereals. Springer, Berlin,
pp 407–456. doi:10.1007/978-3-642-14228-4_10
Nevo E, Beiles A (1989) Genetic diversity of wild emmer
wheat in Israel and Turkey: structure, evolution and
application in breeding. Theor Appl Genet 77:421–455
Nevo E, Chen G (2010) Drought and salt tolerances in wild
relatives for wheat and barley improvement. Plant Cell
Environment 33:670–685. doi:10.1111/j.1365-3040.2009.
02107.x
Nevo E, Korol AB, Beiles A, Fahima T (2002) Evolution of
Wild Emmer and Wheat Improvement: Population
Genetics, Genetic Resources, and Genome Organization
of Wheat’s Progenitor, Triticum dicoccoides. Springer,
Berlin 364
Otto SP, Barton NH (1997) The evolution of recombination:
removing the limits to natural selection. Genetics 147:
879–906
Ozkan H, Brandolini A, Schaefer-Pregl R, Salamini F (2002)
AFLP analysis of a collection of tetraploid wheats indi-
cates the origin of emmer and hard wheat domestication in
southeast Turkey. Mol Biol Evol 19:1797–1801
Ozkan H, Brandolini A, Pozzi C, Effgen S, Wunder J, Salamini F
(2005) A reconsideration of the domestication geography of
tetraploid wheats. Theor Appl Genet 110:1052–1060
Ozkan H, Willcox G, Graner A, Salamini F, Kilian B (2010)
Geographic distribution and domestication of wild emmer
wheat (Triticum dicoccoides). Genet Resour Crop Evol
58:11–53. doi:10.1007/s10722-010-9581-5
Mol Breeding (2011) 28:281–301 299
123
Parsons P (2005) Environments and evolution: interactions
between stress, resource inadequacy and energetic effi-
ciency. Biol Rev 80:589–610
Paterson AH, Lin YR, Li Z, Schertz KF, Doebley JF, Pinson
SRM, Liu SC, Stansel JW, Irvine JE (1995) Convergent
domestication of cereal crops by independent mutations at
corresponding genetic loci. Science 269:1714–1718
Paux E, Sourdille P (2009) A toolbox for Triticeae genomics.
In: Feuillet C, Muehlbauer GJ (eds) Genetics and
genomics of the Triticeae, plant genetics and genomics:
crops and models 7. Springer, Berlin, pp 255–283
Paux E, Sourdille P, Salse J, Saintenac C, Choulet F, Leroy P,
Korol A, Michalak M, Kianian S, Spielmeyer W, Lagudah
E, Somers D, Kilian A, Alaux M, Vautrin S, Berges H,
Eversole K, Appels R, Safar J, Simkova H, Dolezel J,
Bernard M, Feuillet C (2008) Physical map of the
1-Gigabase bread wheat chromosome 3B. Science 322:
101–104
Peng JH, Korol AB, Fahima T, Roder MS, Ronin YI, Li YC,
Nevo E (2000) Molecular genetic maps in wild emmer
wheat, Triticum dicoccoides: genome-wide coverage,
massive negative interference, and putative quasi-linkage.
Genome Res 10:1509–1531
Peng JH, Ronin Y, Fahima T, Roder MS, Li YC, Nevo E,
Korol A (2003) Domestication quantitative trait loci in
Triticum dicoccoides, the progenitor of wheat. Proc Natl
Acad Sci USA 100:2489–2494
Peng JH, Zadeh H, Lazo GR, Gustafson JP, Chao S et al (2004)
Chromosome bin map of expressed sequence tags in ho-
moeologous group 1 of hexaploid wheat and homoeology
with rice and Arabidopsis. Genetics 168:609–623
Perrino P, Laghetti G, D’Antuono LF, Al Ajlouni M, Kan-
bertay M, Szabo AT, Hammer K (1996) Ecogeographical
distribution of hulled wheat species. In: Padulosi S,
Hammer K, Heller J (eds) Hulled wheats. International
Plant Genetic Resources Institute, Rome, pp 102–118
Piperno DR, Weiss E, Holst I, Nadel D (2004) Processing of
wild cereal grains in the Upper Palaeolithic revealed by
starch grain analysis. Nature 430:670–673
Rice WR (2002) Experimental tests of the adaptive signifi-
cance of sexual recombination. Nat Rev Genet 3:241–251
Roder MS, Korzun V, Wendehake K, Plaschke J, Tixier MH
et al (1998) A microsatellite map of wheat. Genetics
149:2007–2023
Rong J, Millet E, Manisterski J, Feldman M (2000) A new
powdery mildew resistance gene: introgression from wild
emmer into common wheat and RFLP-based mapping.
Euphytica 115:121–126
Ross-Ibarra J, Morrell PL, Gaut BS (2007) Plant domestication,
a unique opportunity to identify the genetic basis of
adaptation. Proc Natl Acad Sci USA 104:8641–8648
Rossini L, Vecchietti A, Nicoloso, Stein N, Franzago S, Sal-
amini F, Pozzi C (2006) Candidate genes for barley
mutants involved in plant architecture: an in silicoapproach. Theor Appl Genet 112:1073–1085
Sabot F, Schulman AH (2009) Genomics of transposable ele-
ments in the Triticeae. In: Feuillett C, Muelbauer GJ (eds)
Genetics and genomics of the triticeae, plant genetics
and genomics: crops and models 7. Springer, Berlin,
pp 387–405
Salamini F, Ozkan H, Brandolini A, Schafer-Pregl R, Martin W
(2002) Genetics and geography of wild cereal domesti-
cation in the Near East. Nat Rev Genet 3:429–441
Schuster SC (2008) Next-generation sequencing transforms
today’s biology. Nat Methods 5:16–18
Sears ER (1954) The aneuploids of common wheat. Res Bull
Missouri Agric Exp Stn 572:1–57
Shah M, Gill KS, Bezinger PS, Yen Y, Kaeppler SM, Ari-
yarathne HM (1999) Molecular mapping of loci for
agronomic traits on chromosome 3A of bread wheat. Crop
Sci 39:1728–1732
Sharma H, Waynes J (1980) Inheritance of tough rachis in
crosses of Triticum monococcum and Triticum boeoticum.
J Hered 7:214–216
Simons K, Fellers JP, Trik HN, Zhang Z, Tai YS, Gill BS, Faris
JD (2006) Molecular characterization of the major wheat
domestication gene Q. Genetics 172:547–555
Snape J, Law W, Parker CN, Worland BB, Worland AJ (1985)
Genetical analysis of chromosome 5A of wheat and its
influence on important agronomic characters. Theor Appl
Genet 71:518–526
Sood S, Kuraparthy V, Bai G, Gill BS (2009) The major
threshability genes soft glume (sog) and tenacious glume
(Tg), of diploid and polyploid wheat, trace their origin to
independent mutations at non-orthologous loci. Theor
Appl Genet 119:341–351
Spielmeyer W, Richards RA (2004) Comparative mapping ofwheat chromosome 1AS which contains the tiller inhibi-
tion gene (tin) with rice chromosome 5S. Theor Appl
Genet 109:1303–1310
Stein N (2009) Physical mapping in the Triticeae. In: Feuillet
C, Muehlbauer GJ (eds) Genetics and genomics of the
Triticeae, plant genetics and genomics: crops and models
7. Springer, Berlin, pp 317–335
Tanksley SD, McCouch SR (1997) Seed banks and molecular
maps: unlocking genetic potential from the wild. Science
277:1063–1066
Tanno K, Willcox G (2006) How fast was wild wheat
domesticated? Science 311:1886
Thuillet AC, Bataillon T, Poirier S, Santoni S, David JL (2005)
Estimation of long-term effective population sizes through
the history of Durum wheat using microsatellite data.
Genetics 169:1589–1599
Turner A, Beales J, Faure S, Dunford RP, Laurie DA (2005)
The pseudo-response regulator Ppd-H1 provides adapta-
tion to photoperiod in barley. Science 310:1031–1034
Uauy C, Distelfield A, Fahima T, Blechl A, Dubcovsky J
(2006) A NAC gene regulating senescence improves grain
protein, zinc and iron content in wheat. Science 413:
1298–1301
van Zeist W, Bakker-Heeres JAH (1985) Archaeological
studies in the Levant 1. Neolithic sites in the Damascus
Basin: Aswad, Ghoraife, Ramad. Palaeohistoria 24:
165–256
Villareal R, Mujeeb-Kazi A, Rajaram S (1996) Inherintance of
threshability in synthetic hexaploid by T. aestivumcrosses. Plant Breed 115:407–409
Watanabe N (2005) The occurrence and inheritance of a brittle
rachis phenotype in Italian durum wheat cultivars.
Euphytica 142:247–251
300 Mol Breeding (2011) 28:281–301
123
Watanabe N, Ikebata N (2000) The effects of homoeologous
group 3 chromosomes on grain colour dependent seed
dormancy and brittle rachis in tetraploid wheat. Euphytica
115:215–220
Watanabe N, Sogiyama K, Yamagashi Y, Skata Y (2002)
Comparative telosomic mapping of homoeologous genes
for brittle rachis in tetraploid and hexaploid wheats.
Hereditas 137:180–185
Willcox G (2004) Measuring grain size and identifying Near
Eastern cereal domestication: evidence from the Euphra-
tes valley. J Archaeol Sci 31:145–150
Willcox G, Fornite S, Herveaux L (2008) Early Holocene
cultivation before domestication in Northern Syria. Veget
Hist Archaeobot 17:313–325
Xie W, Nevo E (2008) Wild emmer: genetic resources, gene
mapping and potential for wheat improvement. Euphytica
164:603–614
Yan L, Loukoianov A, Tranquilli G, Helguera M, Fahima T,
Dubcovsky J (2003) Positional cloning of the wheat ver-
nalization gene VRN1. Proc Natl Acad Sci USA
100:6263–6268
Zohary D, Hopf M (2000) Domestication of plants in the old
world. Oxford University Press, Oxford
Mol Breeding (2011) 28:281–301 301
123